Grammatical name- Adjectival clause.
In grammar, an adjectival clause can be characterized as a dependent clause that has a subject and a verb but does not comprehend the entire meaning of the sentence. An adjectival clause begins with a relative pronoun such as that, where, when, or other similar words. In a sentence, an adjectival clause performs the function of an adjective.
When used as an adjectival clause, the phrase "that now prevails" can be found in the preceding sentence. The statement is describing and qualifying the noun 'atmosphere,' which is capitalized. The term refers to the noun 'the atmosphere,' which refers to the atmosphere that was prevalent at the time.